The invention relates to directional boring and, in particular to a system and method for boring through both soil, soft rock and hard rock using the same machine.
At present, when underground utilities such as natural gas, potable water, or sanitary sewer pipes are placed in rock, trenches are excavated using large hard rock trenching equipment such as the Vermeer T-655, or possibly even shot using explosives. In these conditions, electric, telephone and cable TV lines are normally strung overhead along poles, mostly due to the difficulty and expense of placing them underground. Thus, in many situations, a solid rock formation will cause utility lines to be located above ground due to the difficulty of underground installation. Many such sites involve mixed conditions involving both a solid rock formation for part of the run and soil for the remainder, often at the beginning and end of the run. In such a situation, rock drilling or trenching equipment may lack the capability to bore through the soil to reach the rock formation.
Directional boring apparatus for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled though the soil by means of a powerful hydraulic device such as a hydraulic cylinder. See Malzahn, U.S. Pat. Nos. 4,945,999 and 5,070,848, and Cherrington, U.S. Pat. No. 4,697,775 (RE 33,793). The drill string may be pushed and rotated and the same time as described in Dunn, U.S. Pat. No. 4,953,633 and Deken, et al., U.S. Pat. No. 5,242,026. A spade, bit or head configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water to assist in boring.
In one variation of the traditional boring system, a series of drill string rods are used in combination with a percussion tool mounted at the end of the series of rods. The rods can supply a steady pushing force to the impact and the interior of the rods can be used to supply the pneumatic borer with compressed air. See McDonald et al. U.S. Pat. No. 4,694,913. This system has, however, found limited application commercially, perhaps because the drill string tends to buckle when used for pushing if the bore hole is substantially wider than the diameter of the drill string.
Accurate directional boring necessarily requires information regarding the orientation and depth of a cutting or boring tool, which almost inevitably requires that a sensor and transmitting device (xe2x80x9csondexe2x80x9d) be attached to the cutting tool to prevent mis-boring and re-boring. One such device is described in U.S. Pat. No. 5,633,589, the disclosure of which is incorporated herein for all purposes. Baker U.S. Pat. No. 4,867,255 illustrates a steerable directional boring tool utilizing a pneumatic impactor.
Directional boring tools with rock drilling capability are described in Runquist U.S. Pat. No. 5,778,991 and in Cox European Patent Applications Nos. EP 857 852 A2 and EP 857 853 A2. However, although directional boring tools for both rock drilling and soil penetration are known, no prior art device has provided these capabilities in a single machine together with the ability to steer the tool in soil, soft rock and hard rock. Hard rock for purposes of the present invention means rock formations having a compressive strength of 18,000 psi or greater. Concrete typically has a compressive strength of around 8,000 and would be considered xe2x80x9csoft rockxe2x80x9d for this purpose, whereas granite may have a compressive strength of up to 80,000 psi. The present invention addresses this need.
A drill head for an apparatus for directional boring according to the invention includes a bit, a holder for a device for detecting angular orientation of the bit, and a hammer including a striker for delivering impacts to the bit, wherein the bit assembly, holder and hammer are connected head to tail with the bit at a front end. The bit of the invention has a frontwardly facing main cutting surface having a plurality of main cutting teeth disposed thereon and a gage tower extending radially outwardly from the main cutting surface, which gage tower has at least one frontwardly facing gage cutting tooth thereon suitable for cutting over an angle defined by less than a full rotation of the bit. The device for detecting angular orientation is in a predetermined alignment with the gage tower so that it determines the orientation of the gage tower relative to the axis of rotation of the drill head. A starter rod may be used to connect the holder to the string, and the hammer generally follows immediately behind the bit, so that order of components from front to rear is bit, hammer, holder and starter rod. In one preferred embodiment, the main cutting surface is substantially flat and circular and has fluid ejection ports thereon, and the drill head has passages for conducting a drill fluid therethrough to the ejection ports. In another preferred embodiment, the bit has a heel on an outer side surface thereof at a position opposite the gage tower, which heel slopes inwardly from back to front. The heel aids in steering the bit in both rock and soil.
Such a drill head may be used in a method for directional boring according to the invention using a directional boring machine which can push and rotate a drill string having the drill head mounted thereon. Such a method comprises the steps of boring straight through a medium by pushing and rotating the drill head with the drill string while delivering impacts to the bit with the hammer, prior to changing the boring direction, determining the angular orientation of the gage tower using the device for detecting angular orientation, and changing direction during boring by pushing and rotating the bit repeatedly over an angle defined by less than a full rotation of the bit while delivering impacts to the bit with the hammer, so that the drill head deviates in the direction of the cutting action of the gage tower. The medium may be soil, rock, or both at different times during the bore. In particular, the steps of boring straight and changing direction can be carried out in both soil and rock during the same boring run using the same bit. The method and drill head of the invention are especially advantageous for boring wherein the boring run includes hard rock that known soil-rock directional drills cannot penetrate.
According to a further aspect of the invention, a method is provided for directional boring in mixed conditions including both soil and rock. Such a method comprises the steps of (a) boring straight in soil by pushing and rotating the drill head with the drill string, optionally while delivering impacts to the bit with the hammer, (b) boring straight in rock by pushing and rotating the drill head with the drill string while delivering impacts to the bit with the hammer, (c) prior to changing the boring direction in both soil and rock, determining the angular orientation of the gage tower using the device for detecting angular orientation, (d) changing direction when boring in rock by pushing and rotating the bit repeatedly over an angle defined by less than a full rotation of the bit while delivering impacts to the bit with the hammer, so that the drill head deviates in the direction of the cutting action of the gage tower, and (e) changing direction when boring in soil by pushing the bit with the drill string without rotating it so that the drill head deviates in a direction of the gage tower and away from the heel. Since the main cutting face of the drill bit is large and flat, the pushing force of the drill string alone may be insufficient to steer the tool in soft ground without rotation unless a sufficiently sloped heel is provided. It is thus preferred but not essential to deliver impacts to the bit with the hammer while changing direction in soil. This method of the invention may provide better steering in some ground conditions. As noted above, this method is especially advantageous when the mixed conditions include hard rock having a compressive strength exceeding 18,000 psi.
These and other aspects of the invention are described in the detailed description that follows.